1. Field of the Invention
The present invention relates to a core-shell type magnetic particle and a high-frequency magnetic material containing the core-shell type magnetic particle and having magnetic permeability controlled at high frequencies.
2. Description of the Related Art
Magnetic materials are applied in electromagnetic wave absorbers, magnetic ink, inductor and the like, and their importance is increasing year after year. In these magnetic components, permeability real part (μ′) or permeability imaginary part (μ″) are used. For example, both a high μ′ and a low μ″ are used for inductor. A high μ″ is used for electromagnetic wave absorber. Accordingly, when used actually as components, μ′ and μ″ must be controlled according to an operating frequency band of an electronic device. Recently, the operating frequency band of the electronic device is becoming higher, and therefore, the technology for manufacturing materials capable of controlling μ′ and μ″ at high frequency is being demanded.
Magnetic materials for inductor to be used in a high frequency region of 1 MHz include ferrite and amorphous alloy. These magnetic materials show excellent magnetic characteristics, without magnetic loss in a region of 1 MHz to 10 MHz (low μ″), and having a high μ′. In these magnetic materials, however, the permeability real part μ′ is lowered in a higher frequency region of 10 MHz or more, and satisfactory characteristics are not always obtained.
Accordingly, various efforts have been attempted to develop inductance elements by thin film technologies, such as a sputtering method and a plating method, and excellent characteristics in a high frequency region have been confirmed. However, a large apparatus is needed for the thin film technologies such as the sputtering method, and precise control of film thickness and the like is needed. For this reason, the performance is not sufficiently satisfactory in the aspects of cost or yield. Further, the inductor produced by the thin film technology is insufficient in long-term thermal stability of magnetic characteristics in the conditions of high temperature and high humidity.
On the other hand, in the electromagnetic wave absorber, a high μ″ is used to absorb noise generated along with high frequency of an electronic appliance to thereby reduce malfunctions and other problems of electronic devices. Examples of an electronic device include a semiconductor device such as an IC chip, and various communication devices. Such electronic devices are used in a high frequency region from 1 MHz to several GHz, or tens of GHZ or more. Recently, in particular, electronic devices to be used in a high frequency region of 1 GHz or more are increasing in number. Electromagnetic wave absorbers of electronic devices to be used in a high frequency region have been conventionally manufactured by a binder forming method of mixing ferrite particle, carbonyl iron particle, FeAlSi flakes, FeCrAl flakes etc. with resins. In these materials, however, both μ′ and μ″ are extremely low in a high frequency region of 1 GHz or more, and satisfactory characteristics are not always obtained.
Additionally, in materials synthesized by a mechanical alloying method or the like, long-term thermal stability is insufficient, and the yield is low.